Pen



FIG. 1 is a front view of a first embodiment of a pen showing my new design;

FIG. 2 is a back view thereof;

FIG. 3 is a right side view thereof, the left side being a mirror image;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof.

The structure depicted by means of broken lines in FIGS. 1-4, shown for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a pen, as shown and described. 